Presently, as a liquid crystal alignment film for a liquid crystal display device, a rubbing alignment film obtained by rubbing a polyimide resin film is commonly employed. However, by such alignment treatment by a rubbing method, it is difficult to treat a large area uniformly, and fine dust or scratches on the alignment film surface formed by rubbing tend to cause deterioration of the characteristics of the liquid crystal device. As a substitute for the rubbing alignment film, an optical alignment film obtainable by irradiating an organic film with polarized UV rays or the like is being strenuously studied.
As fundamental properties required for the liquid crystal alignment film, it may firstly be mentioned that liquid crystal molecules be aligned uniformly, and an optionally set tilt angle be maintained stably. Further, it will also be important that when it is employed in a liquid crystal device, the voltage retention ratio be high, and the accumulation charge by a DC voltage be low. It is known that such properties are substantially influenced by the composition or molecular structure of the liquid crystal alignment film, and various methods have heretofore been studied for the rubbing alignment film. For example, as a method to increase the tilt angle of liquid crystal molecules in a rubbing alignment film, a method of introducing a long chain alkyl group or a fluoroalkyl group to a side chain of polyimide is known (JP-A-2-282726). Further, as a method to improve the properties such as the voltage retention ratio or the accumulation charge by means of a rubbing alignment film, a method of adding an acryl additive to a polymer alignment film has been proposed (JP-A-6-202118).
On the other hand, an optical alignment film is regarded as a prospective substitute for the rubbing alignment film. However, an optical alignment film fully satisfying the same properties as the rubbing film has not yet been found. Particularly, with respect to the alignment regulating power or the stability for liquid crystal, there are many problems yet to be solved.
The present invention has been made in view of the above-mentioned problems and has an object to provide a liquid crystal alignment treating agent whereby it is possible to obtain a liquid crystal alignment film which presents a high and stable tilt angle of liquid crystal when employed as an optical alignment film, and which is excellent in the charge accumulation property by a DC voltage.